This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-218216 filed on Jul. 18, 2001.
The present invention relates to a sensor, in which a metal electrode having a bonding region is in connect with a metal layer located between a first insulating layer and a second insulating layer through an opening located in the second layer, and a method for manufacturing the sensor.
A sensor, in which a metal layer is located on a diaphragm and a physical quantity is measured on a basis of a variation in a physical characteristic of the metal layer, is proposed. For example, in a proposed flow sensor, a heater and a thermometer are formed using the metal layer made of platinum on the membrane, and the flow rate of a fluid, which flows on the surface of the membrane, is measured by measuring the heat that is transmitted from the thermometer to the fluid or transmitted from the fluid to the thermometer.
Sensors of this type are described by U.S. Pat. No. 5,703,287. In a sensor shown in FIG. 11A, a patterned platinum layer 101 is located between a membrane layer 100 and a passivation layer 102. A metal electrode 103 having a bonding region 105 is in contact with the platinum layer 101 through an opening in the passivation layer 102. In the sensor shown in FIG. 11A, the bonding region 105, where the bonding wire 104 is connected to the metal electrode 103, is located above the opening of the passivation layer 102.
However, in the sensor shown in FIG. 11A, the platinum layer 101 tends to peel due to the stress during a wire bonding operation because the adhesion between the platinum layer 101 and the membrane layer 100 is relatively weak. Therefore, the structure of the bonding region 105 in another sensor shown in FIG. 11B, in which the bonding region 105 is separated from the opening by using the extended metal electrode 103, is preferred in this aspect.
However, the structure of the bonding region 105 in another sensor shown in FIG. 11B has the following problem. In the sensor shown in FIG. 11A, the bonding region 105 is composed of the platinum layer 101 and the metal electrode 103. That is, the thickness of the bonding region 105 is the sum of the thicknesses of the platinum layer 101 and the metal electrode 103. On the other hand, in the sensor shown in FIG. 11B, the bonding region 105 is composed of the metal electrode 103. Therefore, the metal electrode 103 needs to be relatively thicken, for example, approximately one micrometer, to be elastically deformed sufficiently during the wire bonding.
In the case that the metal electrode 103 is substantially made of aluminum, which is commonly used in the semiconductor manufacturing process, aluminum atoms of the metal electrode 103 diffuse into the platinum layer 101 and countless pits, which reach the platinum layer 101, are formed in the metal electrode 103 when the metal electrode 103 and the platinum layer 101 are annealed at about 400xc2x0 C. for the purpose of reducing contact resistance. As a result, wire bonding quality becomes relatively poor in the sensor shown in FIG. 11A, and the electric connection between the platinum layer 101 and the bonding wire 104 becomes relatively poor in the sensor shown in FIG. 11B because the metal electrode 103 tends to break at the edge, which is located at the upper end of the wall that defines the opening, of the passivation layer 102.
The present invention has been made in view of the above aspects with an object to provide a sensor having a desired quality in wire bonding at a bonding region of a metal electrode, which is in contact with a metal layer located between a first insulating layer and a second insulating layer through an opening in the second layer, and to provide a method for manufacturing the sensor.
In the present invention, a sensor includes a first insulating layer, a second insulating layer having an opening, a plurality of metal wirings, and a plurality of electrodes. Each metal wiring has a contacting area, which is located at the bottom of each opening. Each metal wiring is located between the first and second insulating layers except the contacting area. Each electrode has a bonding region located separately from the contacting area. The electrodes are in electrical connect with the contacting areas through the openings. A part of each metal wiring is located beneath each bonding region to provide substantially the same effect as in increasing the thickness of the bonding regions. Therefore, the otherwise thicker bonding region, that is, the otherwise thicker electrode, can be thinned.
The electrodes include any of aluminum, two metals of gold and titan, or three metals of gold, nickel, and titan. When the electrodes include aluminum, the electrodes are annealed such that the surface roughness of the electrode is smaller than 100 angstroms. When the electrodes include two metals of gold and titan or three metals of gold, nickel, and titan, the electrodes are annealed in an atmosphere that a partial pressure of oxygen is lower than 10xe2x88x921 Pa.